Electron discharge device



Jan. 27, 1959 E. c. OKRESS ET AL 2,871,407

ELECTRON DISCHARGE DEVICE Filed A ril 29, 1957 2 Sheets-Sheet 1 ENTORS vM Erne .Okress and k Refocfory Metal Ralph ATTOR NEY E. c. OKRESS ET AL2,871,407

ELECTRON DISCHARGE DEVICE Jan. 27, 1959 2 Sheets-Sheet 2 Filed April 29,1957 Fig. 6.

Refoctory Metal Coating Refoctory Metal Coating Fig.9.

Fig.7.

Fig.ll.

Fig. I3,

Fig. IO.

United States Patent ELECTRON DISCHARGE DEVICE Ernest C. Okress, Eimira,N. Y., and Ralph JMGreen,

Newark, N. 1., a'ssignorsto'westiughouse Electric Corporation,'E'astliittsbnrgh, 11%., a corporation of Penn- :sylvania ApplicationApril 29, 1957,Serial No. 655,731

9 :Claims. .(Cl. BIS-69.69)

This invention relates to electron discharge devices, and moreparticular-1y -to electric spark and arc erosionresistant structuresused in electron discharge devices, particularly of the magnetron type.

In oscillators of the standard magnetron type, ap'lurality of cavityresonators, generally of substantially the same natural frequency, isarranged in a circular manner surrounding a cathode. As a result oftheir-position with respect 'to each other, the cavity resonators areelectrically coupled together and are put-into a-stateof-oscillationbecause of their reaction with 'an electron stream when the magnetron isoperated with an axial magnetic field. It has been found in-theoperation of magnetrous, particularly when used for high power purposes,that electric arcs may "be created'between various elements of themagnetron. Thesearcs tend to erode these elements, and therefore, tendto 'limit'th'e life of the magnetron.

Accordingly, it is an obj'ect'of' this invention'toprovide an improvedspark and are erosion-resistant electron discharge device. 7

It is another object to provide an improved-arc erosionresistantmagnetron.

It is another object to provide an improved anode suitable for use in amagnetron.

These and other objects of our invention will be apparent from thefollowing description taken in accordance with the accompanying drawingsthroughout which like reference characters indicate like parts, whichdrawings form a part of this application, and in which:

Figure l is a top view of theelectrodestructure of a magnetron accordingto one embodiment of our invention;

Fig. 2 is a side sectional view along line IIII of Fig. 1;

.Fig. 3 is a perspective viewof 'aportionof a magnetronsimilar to thatshown in"F-i'gs. 1 and'2 according to one=embodi1nent of our invention;

Fig. =4 is a side sectional view of an 'anode segment of themagnetron-similar to thatshown-in'Figs. l, '2 and 3 according to oneembodiment of oursinvention;

-Fig. 5 is a sidesectional view of-a portion ofan'anode segment i of themagnetron a'ccording *to another embodiment of our invention;

Fig. 6 is --a side Niew of "an anode :segment .of -.the magnetron inaccordance with another embodiment of our invention;

Patented Jan. 27, .1959

2 magnetron shown :in :Fig. 10 along the lines according to oneembodiment of ourinvention;

*Fig. 112 isa :side view of an anode segment of the magnetron shown inFig. 10 taken along line XII'XII according "to another embodiment of ourinvention; and

-Fig."1-3 is aside-viewof the anode segment of "a magnetron similar tothat shown in Fig. 10 taken along lines XILJQI according to stillanother embodiment of our invention.

In Figs. 'l 'and l, there "is shown an electrode structureof-amagnetroniincluding:an anode block 11 having a number of cavityresonators 13 therein. The cavity resonators 13 are separated from .eachother :by anode segment members 15 which delineate'an axial cavity-37.'A cathode 1-7 is positioned in the *center of the axial cavity 37 andincludes -a cathode sleeve member 23 wliih=may be directly heated as inFig. 2 or indirectly heated by an internal heater. In thisparticularembodi-- ment, a cathode sleeve lead member 21 connectsthecathode s'leeve member '23 to an outside voltage source, and acathode '-1eadmember 22 connects a cathode-conductive -mem=ber 33 totheoutside voltage source. For the sake-of simplicity, the externalconnections to the heater lead members and the energy input and output:connections are not-shownin this particular embodiment. Cathode hats 19.are positioned at each end of thecathode sleeve 'memb-er 2-3 to preventelectron leakage from the iuteraction 'space oft-heaxial cavity Thesecathode hats 19 must not be. self-emitting. End plates 25 are positionedat the top and bottom of the mag-- "netron, and a recess -3'lis locatedin the segment end. portions 47.

It-has been fou-nddesirable for the efiicient operation of manymagnetrons to connect the alternate anodeseg-- ments of the magnetron toeach other, and these con neat-ions are known in =the magnetron art asstraps.

' In Figs. ,1 and 2, there is shown a double-strapped magnetron in which.:an inner -strap Z7 is placed in an inner strap groove 39 of the recess31 and is connected to alternate anode segments. An outer strap '29 isplaced over an outer strap groove 41 and is connected to the remainingalternate anode segments. Segment tips 35 are positioned between theinner strap and the cathode in this particular embodiment for reducingthe zero mode field in "the interaction space 37 and 'for the protectionof the strap members. Usually, the anode block 11 is made-of a materialknown as O-FHC (oxygen-free high conductivity) copper. While copper hasthe desirable electrical and thermal conductivity, it has some in'herentdisadvantages as will'be shown.

The magnetronsho-wn in Figs. 1 and 2 is known as a symmetrical magnetronbecause the cavity resonatorslS are of the same shape. With strappedsymmetrical magnetrons, it has been found that the-electric gradientbetween thecathode hats 19 and the anode block 11 is highest 'at thesegment tips 35 of the anode segments :15. Also, most-cathode hats l9and anode segments 15 are contaminated with emission material fromthecathode.

I'n addition, the cathode hats 19 of refractory type cathodes "operatingat relatively high temperature 1500- 1 600 C. B.) generally operate atabout -l000 C. by v-irtue ofintercepted thermal radiation fromthecathode andby direct'thermal conductiontherefrom. When thesemagnetronsareoperating at a high power level,-spurious primary emission,as well as secondary emission from theacathode hats =19, causes'sparksto originate from the cathode-hats 19 which terminate on the segmenttips '35. When "the segment tips are made of copper, the terminationofthe spark on the tip 35 may quickly reach temperatures at whichthecopper begins to melt and evaporate. "The acopper .icns so formed becomethe source of an electric are between the cathode hat 19 and the segmenttip 35. This electric arc causes erosion of the segment tip and leads toshortened life power limitation and eventual total failure of themagnetron.

Also, in high power magnetrons, the electrons from the cathode 17 mayimpinge on the inner strap 27, and portions of the sides of the segmenttips 35, causing secondary electron emission which, in turn, may lead tosparking and arcing between the inner strap 27 and the segment tip 35with the attendant melting and erosion of these members. The are betweenthe cathode hat 19 and the segment tip 35 is an essentially directcurrent are and that between the segment tip 35 and the inner strap 27is exclusively an alternating current (microwave) arc.

In order to fulfill the requirements for high power operation inmagnetrons, it is necessary to eliminate existing limitations resultingin arcing of the magnetrons, particularly during long pulses. Therefore,besides reducing the emissive constituent in the cathode to a minimumconsistent with maintenance of space charge emission, we propose toreplace portions of the magnetron electrodes with refractory materialswhich have are erosion-resistant properties.

These refractory materials should have a high thermal diffusivity(between that of copper or silver and tungsten), a low vapor pressureand evaporation rate as a function of temperature (comparable to that ofmolybdenum or preferably tungsten, which have vapor pressures at 2000 K.of 7189x10 mm. Hg and 6.45 l" mm. Hg respectively and evaporation ratesat 2000" K. of l.00 l0- gm./cm. /sec. and l.l14 10 gm./cm. /sec.respectively), low secondary emission properties (between those oftungsten and carbon-between 1 and 1.5 maximum regardless of the stickingpotentials or incidence angle) and a melting point of 2340 C. or above.It should be noted that the melting point of copper is only 1084 C.,while tungsten melts at 3387 C. Also, while copper has a vapor pressureof about l0 micron Hg at 1035 C., tungsten has a vapor pressure of about10* micron I-Ig at the high temperature of 2554 C.

Consideration of the melting points, vapor pressure and rates ofevaporation, thermal diffusivity and sec ondary emissive properties marktungsten (Wolfram) as a very suitable refractory material. Othersuitable refractory materials include molybdenum, tantalum, ruthenium,osmium and iridium and their alloys.

If portions of the electrode, such as the segment tips 35, the innerstraps 27 and other portions of the anode segments 15, as will bediscussed below, are made of these refractory materials, the erosion ofthe surfaces due to arcing is markedly reduced or eliminated. Becausethese surfaces are not so easily vaporized, the tendency from a spark todevelop into a metallic arc is reduced.

In order to more clearly illustrate the portions of the electrodesinvolved, there is shown in Fig. 3 a perspective view of a portion of amagnetron similar to that shown in Figs. 1 and 2. A portion of the anodeblock 11 is shown including anode segment members 15 which separatecavity resonators 13 from each other. Also, a portion of the axialcavity 37 in which the cathode 17 is located is shown. The cathodesleeve member 23 is normally coated with a suitable emissive material,if indirectly heated. lf directly heated, the heating current isconducted directly through the emissive material composed of thoria anda refractory metal power such as molybdenum or tungsten. The cathode hat19, shown in Fig. 2, is not shown in Pig. 3 for the purpose of clarityand simplicity. In the segment end portion 47, there is shown a recess31 including an inner strap groove 39 in which the inner strap 27 may beplaced and an outer strap groove 41 in which an outer strap 29 may beplaced. In this particular segment, the outer strap is not connected tothe anode segment 15 shown in section, but is connected to the otheradjacent alternate anode segments. Also shown is the anode segment innerface 43 and the anode segment tip As can be seen, the segment tip inner4 face 45 is really an extension of the anode segment inner face 43.

In Fig. 4, there is shown a side view of a portion of an anode segment15 similar to that shown in Fig. 3, in which the segment tip 35 and aportion of the recess 31 is made of a suitable refractory material. Inthis particular embodiment, the segment tip 35 is made separately fromthe anode segment 15. For example, if the segment tip 35 is made ofmolybdenum, it may be joined to the copper anode segment 15 by asuitable brazing alloy 15, such as a gold-c0pper eutectic alloy which isbrazed to the molybdenum which has been nickel-plated and sintered. Iftungsten is used as a refractory material, a gold-nickel eutecticbrazing material has been found to be particularly suitable because ofits higher melting point and because it will join the tungsten directlyto the copper without an additional plating operation. It may sometimesbe desirable to make only the segment tip 35 (the part to the left ofthe dotted line in Fig. 4) of refractory material and not include thatpart of the recess 31 shown in Fig. 4. Also, as shown in Fig. 4, theinner strap 27 may also be made of the refractory material, if desired.In any case, the outer strap 29 is made of (OFHC) copper as it is notusually affected as much by arcing as the other electrodes. Theserefractory materials have higher melting points than the copper, aspointed out previously, and have a lower vapor pressure than copper,which is also desirable. However, their thermal diffusivity and theirelectrical conductivity while still good, are lower than copper.

In Fig. 5, there is shown a side view of an anode segment similar tothat shown in Fig. 3 in which the inner strap member 27 and the outerstrap member 29 are located completely within the recess 31 so that thetop surface of the two straps is below thev segment end po tion 47. Acover plate 49, which in this particular embodiment is an integral partof the segment tip 35, has been placed over the top of the recess 31,but does not extend appreciably over the space between the anode segmentmembers 15. In this embodiment, the inner strap 27, the segment tip 35,portions of the bottom of the recess 31 and the cover plate 45 are madeof a suitable refractory material. This cover plate 49 has the advantageof increasing the thermal cross section for better heat conduction fromthe segment tip 35. As seen in both Figs. 4 and 5, the segment tip innerface 45 is made of a refractory material which reduces erosion due toany arcing tendency between the cathode hat 19 and the segment tip 35.The inner strap 27 may also be of a refractory material, if desired.

It may be advantageous, especially if the high thermal diffusivity andelectrical conductivity of copper is particularly desirable, to coat thesurface of the segment tips 35 and possibly, but not necessarily, theinner strap 27 with a suitable refractory material rather than make theinner strap and the segment tip 35 entirely of the refractory. We havefound that a particularly suitable embodiment is that shown in Fig. 6,in which a side view of an anode segment similar to that shown in Fig. 3is shown. In addition to the anode segment tip 35, certain portions ofthe bottom recesses 31 and the top, inner and bottom surfaces of theinner strap 27 may be coated with a refractory material. Also, in thisparticular embodiment, the entire segment inner face 43 has also beencoated with a refractory material. Of course, if desired, only the anodesegment tip 35 may be coated rather than the entire segment inner face43.

One method we have found particularly suitable is to plate a very thin(1 l0- inch) layer of gold on the copper base and then plate a layer(0003-0005 inch thick of rhodium on the gold. This plating forms a goodbond to the gold-plated copper and has the advantages of having the highmelting point and low vapor pressure of the refractory metal rhodiumwith the excellent thermal plated portions.

difiusivity of the base metal copper. f course other suitable@refractory materials may be plated on-ithe' copper.

A top view of the "plated anode segment .15 .of Fig.

'6 is shown in Fig. 7 to more clearly pointou-t the -plated portions. InFigs. 6 and 7, the-innerstrapZT-is notsconnected to the particular anodesegment .15 which-isrshown but :is'connected tothe alternate anodesegments. ,However, if strapping is used on the bottom-endoftheanodesegment 15, the bottom inner strap would be connected to the anodesegment shown, and "the bottom outer strap 29 would not beconnected tothe anode segment '15-shown. 4 I

'In Fig. 8, there is-shown-a side viewof-.an:anode.seg inentinwhich theinner strap 27 is-c'onnectedto the anode segment 15 .in which thesegment inner face 43, all surfaces of the segment tip .351and the innerand upper surfaeesof the inner strap -27 have been .plated with asuitable refractory-material.

In Fig. 9, there is shown atop view-'o'fthe platedanode segment shown inFig. -8 to more clearly ,point .outLthe Of :course, there are otherembodiments which .-may

be used in plating or making the portions :of the .electrodes which aresubject-to arcing, of-refractory-metals.

For example, it'may be desirable .not toqplatevtheportions of therinnerstrap member 27.s hown as plated-in Figs; 6-9, even though other partsare plated .as shown in those figures. In some instances, .the-entireanode segment inner face *43 .may .be .madeor'p'lated .with ;arefractory metal. While in others, only portions of .the

segment inner face 43 are plated, :for -example,.only .the

segmenttip-metal face 45. Also, in some instances, the

-.cover-,p late'49, similar to that shown .in .Fig. 5,.may be separatefrom the segmentt-ip .315 and, .ifdesircd, .may

be made-of another material or may .bemade of copper.

not of similar size) magnetron, such-as1that knowntas the "rising sunmagnetron, straps are not used. vlI-Iov'vever, our invention maybe usedin a rising sun magnetron, the anode of which is shown in Fig. 10. Ascan be seen, the anode block 49 which, as in most magnetrons, is made ofOFHC copper, is provided with a number of cavity resonators. However, incontrast to the cavity resonators shown in Figs. 1 and 2, these cavityresonators are made alternately large 53 and small 51. Also, the cavityresonators 51, 53 are separated by anode segment members 57, the innerfaces 59 of which delineate an axial cavity 55 in which a cathode isnormally positioned. In this particular figure, however, the cathode isnot shown for purposes of clarity. Depending on the power used and otherfactors, it is desirable to make or plate certain portions of thesegment members with a refractory metal, such as those discussed above.

In Fig. 11, there is shown a side view of an anode segment member 57taken along lines XIXI in which the entire anode segment member 57 ismade of a suitable refractory material such as tungsten. As can be seen,the side portions 611, the inner face portions 59 and the end portions65 are all of a refractory material. In this case, as in the cases ofFigs. 12 and 13, only one anode segment member 57 is shown, but it isunderstood that all segment members 57 are the same in any onemagnetron.

In Fig. 12, there is shown a side view of an anode segment member 57taken along lines XIIX[I in which only a small part of the inner portionof the segment member 57 is made of or plated with a refractory metal.However, the entire segment inner face 59 of the segment member 57 ismade of or coated with a refractory metal.

In Fig. 13, there is shown a side view of another anode tions 63 .areof.the refractory metal.

segment member 57 also taken along l ines XIL-IXlilin which the-entiresegment inner;face.59 .isno'tmade of a refractory metal but ,onlythesegmenttinner face end por- Of course, =anumher-of variations might bemade in Figs. 1.0 through 13 depending on'the areas in which the .arcswould tend to form.

Also, it is understood that while our invention using refractoryelements has been shown as used with a magnetron, it may be used inother electron discharge devices in whichsarcs tend .to form and therebyerode metal electrodes, for example, ..in klystrons, traveling wavetubes, 'carsinotrons, .stabilitrons, etc.

While-the present inventionhas -.been shown in a few forms only, it willbe :obvious to those skiIled in the ar-t thatit is not so limited'butdssusceptible of various changes and modifications without distinguishingfrom the .spirit and scopethereof.

We claim as ourinvention:

1. A magnetron having a plurality of electrodes, two of said electrodeshaving .a :high potential gradient be- -tween.them, portions-of.the-surface ofrsaid'two electrodes which are subject-to an alternatingcurrent electric arc formation between them being composed of arefractory .metallic material.

2. .A .magnetron having a ,pluralityof electrodes, two

of rsaid electrodes having a .high ;p.otential gradient 'between them,port-ionsof the surface of said two electrodes which are subject toanalternating current electric arc formation between them being composedof va-refractory -metallic material havingamelting pointabove 2340 C.

.3. A'magnetron :having.a;plurality of electrodes, two

of said electrodes having :a .high .potential gradient 'beiridium,andtheir alloys.

4. A magnetron including. ananodeha-ving .anaxial ;cavity and.a. plur=ality ofcavity resonators radiating there- ,from, .a cathodelocatedwithin said ax-ial cavity, said caviitytresonators being separated byanode, segmentmembers,

said segment members having aninner face adjacent said axial cavity,said segment members including an end portion having a recess therein,said segment members having a segment tip member between said recess andsaid axial cavity, said segment tip member having a tip inner faceconstituting a portion of said segment inner face, and a metallic strapmember connected to alternate segment members of said anode, saidmetallic strap member having an inner surface facing toward said segmenttip member, said metallic strap member being positioned within saidrecess, said tip member face and said inner surface of said metallicstrap member being composed of a refractory metallic material having amelting point above 2340 C.

5. A magnetron including an anode having an axial cavity and a pluralityof cavity resonators radiating therefrom, a cathode located within saidaxial cavity, said cavity resonators being separated by anode segmentmembers, said segment members having an inner face adjacent said axialcavity, said segment members including an end portion having a recesstherein, said segment members having a segment tip member between saidrecess and said axial cavity, said segment tip member having a tip innerface constituting a portion of said segment inner face, and a metallicstrap member connected to alternate segment members of said anode, saidmetallic strap member having an inner surface facing toward said segmenttip member, said metallic strap member being positioned within saidrecess, said tip inner face and said inner surface of said metallicstrap member being composed of a refractory metallic material selectedfrom the group consisting of tungsten,

7 molydenum, tantalum, ruthenium, osmium, iridium, and their alloys.

6. A magnetron including an anode having an axial cavity and a pluralityof cavity resonators radiating therefrom, a cathode located within saidaxial cavity, said cavity resonators being separated by anode segmentmembers, said segment members having an inner face adjacent said axialcavity, said segment members including an end portion having a recesstherein, said segment members having a segment tip member between saidrecess and said axial cavity, said segment tip member having a tip innerface constituting a portion of said segment inner face, a metallic strapmember connected to alternate segment members of said anode, saidmetallic strap member having an inner surface facing toward said segmenttip member, said metallic strap member being positioned Within saidrecess, and a cover plate covering said recess, said tip inner face andsaid inner surface of said metallic strap member being composed of arefractory metallic material having a melting point above 2340 C.

7. A magnetron including an anode having an axial cavity and a pluralityof cavity resonators radiating therefrom, a cathode located Within saidaxial cavity, said cavity resonators being separated by anode segmentmembers, said segment members having an inner face adjacent said axialcavity, said segment members ineluding an end portion having a recesstherein, said segment members having a segment tip member between saidrecess and said axial cavity, said segment tip member having a tip innerface constituting a portion of said segment inner face, a metallic strapmember connected to alternate segment members of said anode, saidmetallic strap member having an inner surface facing toward said segmenttip member, said metallic strap member being positioned within saidrecess, and a cover plate covering said recess, said tip inner face andsaid inner surface of said metallic strap member being composed of arefractory metallic material selected from the group consisting oftungsten, molydenum, tantalum, ruthenium, osmium, iridium, and theiralloys.

8. A magnetron including an anode having an axial cavity and a pluralityof cavity resonators radiating therefrom, a cathode located Within saidaxial cavity,

said cavity resonators being separated by anode segment members, saidsegment members having an inner face adjacent said axial cavity, saidsegment members including an end portion having a recess therein, saidsegment members having a segment tip member between said recess and saidaxial cavity, said segment tip member having a tip inner faceconstituting a portion of said segment inner face, a metallic strapmember connected to alternate segment members of said anode, saidmetallic strap member having an inner surface facing toward said segmenttip member, said metallic strap member being positioned within saidrecess, and a cover plate covering said recess, said cover plate havinga top surface, said tip inner face, said top surface of said cover plateand said inner surface of said metallic strap member being composed of arefractory metallic material having a melting point above 2340 C.

9. A magnetron including an anode having an axial cavity and a pluralityof cavity resonators radiating therefrom, a cathode located Within saidaxial cavity, said cavity resonators being separated by anode segmentmembers, said segment members having an inner face adjacent said axialcavity, said segment members including an end portion having a recesstherein, said segment members having a segment tip member between saidrecess and said axial cavity, said segment tip member having a tip innerface constituting a portion of said segment inner face, a metallicstrapmember connected to alternate segment members of said anode, saidmetallic strap member having an inner surface facing toward said segmenttip member, said metallic strap member being positioned within saidrecess, and a cover plate covering said recess, said cover plate havinga top surface, said tip inner face, said top surface of said cover plateand said inner surface of said metallic strap member being composed of arefractory metallic material selected from the group consisting oftungsten, molybdenum, tantalum, ruthenium, osmium, iridium, and theiralloys.

References Cited in the file .of this patent UNITED STATES PATENTSWooten Dec. 26, 1950

